The invention relates to fibers made of cellulose derivatives and to fibers made of cellulose regenerated from these derivatives.
"Cellulose derivatives" is here understood to mean, in a known way, the compounds formed, as a result of chemical reactions, by substitution of the hydroxyl groups of cellulose, these derivatives also being known as substitution derivatives. "Regenerated cellulose" is understood to mean a cellulose obtained by a regeneration treatment carried out on a cellulose derivative.
The invention more particularly relates to fibers made of cellulose formate and to fibers made of cellulose regenerated from this formate, and to the methods for producing such fibers.
Fibers made of cellulose formate and fibers made of cellulose regenerated from this formate have been described in particular in International Patent Application WO 85/05115 (PCT/CH85/00065), filed by the Applicant Company, or in the equivalent Patents EP-B-179,822 and U.S. Pat. No. 4,839,113. These documents describe the production of spinning solutions based on cellulose formate by reaction of cellulose with formic acid and phosphoric acid. These solutions are optically anisotropic, that is to say that they exhibit a liquid crystal state. These documents also describe the cellulose formate fibers obtained by spinning these solutions, according to the so-called dry-jet-wet spinning technique, and the cellulose fibers obtained after a regeneration treatment of these formate fibers.
In comparison with conventional cellulose fibers, such as rayon or viscose fibers, or with other conventional non-cellulose fibers, such as nylon or polyester fibers, for example, all spun from optically isotropic liquids, the cellulose fibers of Application WO 85/05115 are characterized by a much more orderly structure, due to the liquid crystal nature of the spinning solutions from which they emerge. They thus exhibit very high mechanical properties in extension, in particular very high tenacity and modulus values, but, on the other hand, are characterized by rather low values of elongation at break, these values being on average between 3% and 4% and not exceeding 4.5%.
However, greater values of elongation at break may be desirable when such fibers are used in certain technical applications, in particular as components for reinforcing a tire, in particular a tire carcass casing.